The invention relates to a disc brake and, in particular, to a disc brake for a commercial vehicle having a caliper which straddles a brake disc and is fastened axially displaceably, in relation to the brake disc, to a brake carrier by two fastening elements. The fastening elements have, in each case, one guide spar which is connected fixedly to the brake carrier, one guide spar is guided in a plain bearing configured as a floating bearing and another is guided in a plain bearing configured as a fixed bearing, for the axial displaceability of the caliper.
In such disc brakes, which are also called “sliding caliper” disc brakes, the caliper is connected to a brake carrier on the vehicle side by the fastening elements.
Here, guide spars are usually connected to the brake carrier by being screwed, which guide spars are guided on the other side in sliding bearings of the caliper such that an axial displacement of the caliper with respect to the stationary brake carrier is possible. While one of the sliding bearings is configured as a fixed bearing with a small amount of sliding play, the other acts as a floating bearing, as a result of which, in particular, manufacturing tolerances are compensated for.
In addition to the guide spar, the fixed or locating bearing includes a guide sleeve, preferably made from brass, which is pressed fixedly into the caliper and is guided together with the caliper so as to slide on the guide spar.
Since, however, play-free sliding mounting between the guide spar and the guide sleeve cannot be realized in practice, the caliper remains radially movable to a certain extent under operating conditions, with the result that, in this case, rattling noise is produced in many cases, which is considered disruptive, above all in vehicles which are used for passenger transport.
Moreover, on account of the radial movability in the fixed bearing, deflection of the guide sleeve can occur, by way of which the operational security of the entire disc brake is impaired.
Irrespective of the type of sliding bearings, the fixed bearing has to be sealed in order to protect against corrosion and dirt. However, dirt particles nevertheless pass between the guide sleeve and the guide spar, which naturally impairs the sliding properties, in particular, of the guide sleeve which is composed of brass.
The invention is therefore based on providing a disc brake such that the wear and shaking resistance of the fixed bearing is improved with low structural and manufacturing outlay.
According to the invention, a disc brake includes a caliper which straddles a brake disc and is fastened axially displaceably, in relation to the brake disc, to a brake carrier by two fastening elements. The fastening elements have, in each case, one guide spar which is connected fixedly to the brake carrier, one guide spar is guided in a plain bearing configured as a floating bearing and another is guided in a plain bearing configured as a fixed bearing, for the axial displaceability of the caliper. The guide spar of the fixed bearing has, on an outer circumference, a radially elastically deformable section, against which the associated bearing bears at least in some sections.
A disc brake configured in this manner is distinguished, in particular, by the fact that the guide spar is always held under slight prestress with respect to the caliper. As a result, first rattling is prevented in the guide and, second, manufacturing tolerances can be compensated for without problems in the entire assembly.
There is provision according to one advantageous development of the invention to manufacture and to mount the radially elastically deformable section of the guide spar as a separate component. Here, this section is configured as a damping bush, having a metallic inner casing which serves as a carrier for an elastically deformable layer, for example rubber, which is pressed together with the metal bush.
Here, the caliper or its guide sleeve bears slidably as a sliding bearing against the elastic layer, it being possible for the sliding force which is to be applied to be set by the selection of the elastic material, but also by the dimensions, in particular of the diameter, which define the pressing forces.
If a correspondingly great braking moment is introduced, the elastic layer is compressed to such an extent that the sliding bearing also comes into contact with the guide spar outside the elastic layer. However, damage of the layer or the sleeve overall does not occur in this case.
The damping bush is preferably arranged on the guide spar with axial play. For simple mounting of the damping bush and likewise in order to set the axial play, a circumferential shoulder, against which the damping bush bears with an end side, is provided on the guide spar. The damping bush is secured against movement by a closure ring which is assigned to the other end side and is connected to the guide spar on the end side, to be precise on that end of the guide spar which faces away from the brake disc.
The sliding bearing region is usually sealed at that end of the guide spar which faces the brake disc by use of a folding bellows, which is fastened on one side to the guide spar and on the other side to the caliper.
According to one advantageous development of the invention, the damping bush has a progressive damping characteristic in the radial load direction, which progressive damping characteristic preferably differs over the part regions.
To this end, the damping bush can be provided, on the outside and/or inside, with webs which are arranged parallel to one another and at a spacing from one another and which in each case form lateral limits for grooves, the flanks of the webs opening into contact regions, on which the guide spar is supported or which bear against the guide sleeve.
At least one part of the webs may be thicker, wider, and/or at a different spacing from one another. The webs can extend axially, circumferentially or diagonally.
In the case of increased radial forces which occur as a result of operation, as occur, for example, when driving on damaged roads, the webs are compressed correspondingly, with the result that the damping bush stiffens abruptly. This produces a progression stage which leads to a noticeably improved damping characteristic, with the consequence that, even in these cases, rattling is largely avoided, as is produced by the guide sleeve and the guide spar striking one another.
This naturally contributes to an increase in the service life of the locating bearing, since the guide sleeve and the guide spar are loaded to a less pronounced extent.
The widths of the inner grooves which are equally large or different, depending on the requirement and design, are preferably narrower than the grooves on the outside. In the case of corresponding radial loading, the inner webs, which are formed by the grooves, can be deformed to such an extent that, together with the grooves, they form a closed or largely closed surface area in the region of the active radial forces.
Otherwise, the grooves are preferably of an arcuate design in cross section, while the webs can be adapted with their contact faces to the curvature of the guide sleeve or the guide spar.
For additional damping, that is to say prevention of the production of rattling noise, there is provision according to a further aspect of the invention, to arrange a damping ring in the region of the folding bellows. The damping ring is connected to the folding bellows on the inside of the latter and engages around the guide spar.
The damping bush and the damping ring can be installed without problems into disc brakes which are in use, to which end only the guide spar and, optionally, the inner folding bellows have to be exchanged. This expediently takes place during a brake pad change.
As mentioned, the damping bush is mounted on the guide spar with axial play. Here, the play can be determined by an adjustment of the closure ring, depending on how the latter is positioned on the guide spar. The axial play of the damping bush preferably corresponds to half the air play, in order to always ensure the freedom of movement of a reaction-side brake pad.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of one or more preferred embodiments when considered in conjunction with the accompanying drawings.